The present invention relates generally to methods and devices that use nonlinear elements to receive data. More particularly, the present invention relates to systems that provide adaptive compensation for such nonlinearity.
Data retrieval performance requirements are advancing at a phenomenal rate. Mass storage device capacities grow at an average rate of more than 50% per year. Device access times and power consumption levels are also generally shrinking. Because of these requirements and similar advancements in other fields of technology, the use of higher-performing nonlinear elements has proliferated.
For an integrated circuit (IC) at the read channel output to interpret data from nonlinear elements correctly and at very high data rates, nonlinearity compensation systems have been developed. These systems introduce a signal, synchronized with the read signal, to offset the nonlinearity enough to make the read signal intelligible to the channel IC.
Stringent system requirements have necessitated further improvements in this nonlinearity compensation, however. Magneto-resistive (MR) elements, for example, can change state with temperature changes, electrical fluctuations, asperities, and fractured (i.e. multiple-domain) fields. These state changes can prevent an MR device from reading correctly for significant periods of time. Modern giant magneto-resistive transducers and dual stripe devices are particularly vulnerable to this type of problem.
Some relief is obtained from adaptive nonlinearity adjustment systems such as that depicted in U.S. Pat. No. 5,744,993 (xe2x80x9cRead Channel for at Least Partially Offsetting Nonlinear Signal Effects Associated with the Use of Magneto-Resistive Headsxe2x80x9d filed Sep. 27, 1995 by Jeffrey Lee Sonntag). These systems detect a measure of how much nonlinearity is in the signal received by the channel IC, and adjust the compensation to make it lower. Further relief from this problem is obtained by error correction routines. In a 1024-byte block, for example, present-day routines can correct for up to about 32 bytes of erroneous data, without re-reading. Thus, a nonlinear element in an unknown state can afford to mis-read up to about 32 bytes of data at the beginning of a sector before the error becomes non-correctable. Unfortunately, this is often much too short a time in which to compensate for a large state change. Such systems often require many re-read attempts to be successful, or fail entirely.
Existing adaptive nonlinearity compensation schemes are only satisfactory for very slow state changes. They are poorly suited for rapid state changes or for large state changes which can occur when a read element is not used for a substantial period of time. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
The present invention comprises devices and methods for recovering a block of stored data that has been erroneously read due to improper read head nonlinearity compensation. Systems of the present invention typically provide compensation sufficient to allow a channel IC to interpret a read signal correctly within about 4% of the block read duration. Thus, the present invention typically prevents such improper compensation from causing large numbers of erroneous bytes to be read. With the present invention, error recovery is usually possible by re-reading the block only once.
In accordance with one embodiment of the invention, an electro-mechanical system is described in which a nominal rate of compensation adjustment is derived according to methods such as are known in the art. A controller then up-shifts the rate of adaptation by more than twice the nominal rate while a read element reads a first portion of the data block. Subsequently, the controller down-shifts the rate of adaptation to a lower rate allowing stable compensation for most of the remaining bytes of the block.
Systems of the present invention optionally provide data stored in a memory device from which the controller derives initial compensation values, routines to down-shift the rate of adaptation in stages or continuously, and simple and iterative ranging.
The present invention also can be implemented as a computer-readable program storage device which tangibly embodies a program of instructions executable by a computer system to perform a gear-shifting adaptive compensation method as described above.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.